The present invention generally relates to delay time control apparatus for controlling delay times at the time of a changed speed reproduction mode, and more particularly to a delay time control apparatus for controlling one or two delay times of one or two delay circuits which delay a reproduced signal from a rotary head. A magnetic tape which is played, is recorded at the time of a recording mode by rotary heads having gaps of mutually different azimuth angles, and is at least recorded with a frequency modulated video signal. The magnetic tape has a track pattern in which recorded positions of horizontal synchronizing signals on two mutually adjacent tracks are not aligned in the width direction of the tracks and are shifted in the longitudinal direction of the tracks. The delay time control apparatus according to the present invention controls the one or two delay times so that it is possible to obtain a stable reproduced signal accompanying no skew phenomenon and having no color disappearance at the time of the change speed reproduction mode in which the magnetic tape moves at a tape speed different from the tape speed at the time of the recording mode. The skew phenomenon and the color disappearance will be described later on in the specification.
A magnetic recording and reproducing apparatus (video tape recorder or VTR) employing the azimuth recording and reproducing system, is well known. A magnetic tape which is recorded in a standard mode of the VTR, usually has a track pattern in which recorded positions of horizontal synchronizing signals on two mutually adjacent tracks are aligned in the width direction of the tracks (so-called H-alignment). Accordingly, in a case where a PAL system color video signal is recorded on the magnetic tape, for example, the recorded positions of the horizontal synchronizing signals on two mutually adjacent tracks are aligned in the width direction of the tracks. Moreover, in this case, recorded sections of one horizontal scanning period (1H), containing modulated waves obtained by modulating chrominance subcarriers having inverted phases by color difference signals (R-Y), are also recorded on the mutually adjacent tracks in alignment along the width direction of the tracks.
Recently, the recording and reproducing time of the VTR has become extended. When extending the recording and reproducing time, the length of the magnetic tape, the diameter of a drum, and the length of the track on which the video signal is recorded, remain unchanged. The track widths of rotary heads are made extremely narrow, and the tape speed is reduced to 1/2 the tape speed of the standard mode, for example, so as to extend the recording time to twice the recording time which is obtainable in the standard mode. In this case, a difference between starting positions of two mutually adjacent tracks becomes equal to 1/2 the difference between starting positions of two mutually adjacent tracks which are formed at the time of the standard mode. As a result, the H-alignment does not exist in the track pattern which is formed during an extended time mode in which the recording time is extended. Accordingly, in the track pattern which is formed during the extended time mode, the recorded sections of 1H, containing the modulated waves obtained by modulating the chrominance subcarriers having the inverted phases by the color difference signals (R-Y), are recorded on the mutually adjacent tracks in non-alignment along the width direction of the tracks.
The existence of the H-alignment in the track pattern formed on the magnetic tape, greatly affects a so-called changed speed reproduction mode (or special reproduction mode) in which the magnetic tape moves at a tape speed which is different from the tape speed at the time of the recording mode. In other words, because the tape speed at the time of the change speed reproduction mode is different from the tape speed at the time of the recording mode, a scanning locus of one rotary head crosses over a plurality of tracks. Hence, in addition to tracks which are pre-recorded by a rotary head having a gap of the same azimuth angle as the gap of the reproducing rotary head, the reproducing rotary head also scans over reverse tracks which are pre-recorded by a rotary head having a gap of an azimuth angle different from the azimuth angle of the gap of the reproducing rotary head. In other words, a so-called reverse or opposite tracking takes place. When a large portion of an area on the magnetic tape in contact with the reproducing rotary head belongs to the reverse track, there is a great decrease in the level of the reproduced signal due to the azimuth loss effect, and a noise bar is generated in the reproduced picture.
However, in a case where the magnetic tape is pre-recorded in the standard mode so that the H-alignment exists and the changed speed reproduction is carried out with this magnetic tape, the horizontal synchronizing signals are constantly reproduced with an interval of 1H. In addition, the color difference signals (R-Y) are reproduced so that the recorded section of 1H containing the carrier having the inverted phase and the recorded section of 1H containing the carrier having the non-inverted phase are alternately reproduced. For this reason, the reproduced PAL system color video signal is the same as the pre-recorded PAL system color video signal, as to the periodicity of the reproduced horizontal synchronizing signals and the sequence of the reproduced carrier chrominance signals.
On the other hand, in a case where the changed speed reproduction is carried out with respect to a magnetic tape which is recorded in the extended time mode and has a track pattern in which the H-alignment does not exist, the noise bar is generated in the reproduced signal from the reproducing rotary head when a large portion of the area on the magnetic tape in contact with the reproducing rotary head belongs to the reverse track. In addition, the interval of the reproduced horizontal synchronizing signals becomes equal to 1H/2, for example, and the sequence of the reproduced carrier chrominance signals becomes disordered. For this reason, when carrying out the changed speed reproduction with respect to the magnetic tape having the track pattern in which the H-alignment does not exist, the periodicity of the reproduced horizontal synchronizing signal becomes disordered as the reproducing rotary head scans across the reverse track. Hence, when the reproduced frequency modulated video signal is simply subjected to a frequency demodulation and is then supplied to a monitoring display device, the reproduced picture will be distorted in the horizontal direction of the picture (so-called skew phenomenon), and the color disappears at a part of the reproduced picture (hereinafter referred to as a color disappearance). As a result, it is only possible to obtain a reproduced picture having a poor picture quality.
Accordingly, in a conventional apparatus, a skew part of a reproduced luminance signal, wherein a skew of 1H/2 is generated, is detected in a 1H/2 skew detecting circuit. An output detection signal of the 1H/2 skew detecting circuit is supplied to a first switching circuit as a first switching signal. The first switching circuit selectively produces one of a reproduced color video signal in which the reproduced luminance signal and a reproduced carrier chrominance signal of the PAL system, for example, is multiplexed, and a delayed reproduced color video signal which is obtained by delaying the reproduced color video signal by a delay time of 1H/2 in a 1H/2-delay circuit. In a state where the first switching circuit is producing one of the reproduced color video signal and the delayed color video signal, the first switching circuit is switched to produce the other of the reproduced color video signal and the delayed color video signal, responsive to the first switching signal (the output detection signal of the 1H/2 skew detecting circuit). Thus, a reproduced color video signal in which the periodicity of the reproduced horizontal synchronizing signal is maintained, is produced from the first switching circuit.
A color burst signal is extracted from the above reproduced color video signal, and the phase of the extracted color burst signal is detected in a phase detecting circuit. In a case where the sequence of the reproduced carrier chrominance signals is correct, a square wave which is inverted for every 1H is obtained from the phase detecting circuit. However, in a case where the sequence of the reproduced carrier chrominance signals (chrominance sequence) is incorrect, the periodicity of the output signal of the phase detecting circuit is disordered. A chrominance sequence discriminating circuit receives the output signal of the phase detecting circuit, and discriminates a disorder in the chrominance sequence from a disorder in the periodicity of the output signal of the phase detecting circuit. An output signal of the chrominance sequence discriminating circuit is supplied to a second switching circuit as a second switching signal. The second switching circuit is designed to selectively produce one of the reproduced carrier chrominance signal and a delayed reproduced carrier chrominance signal which is obtained by delaying the reproduced carrier chrominance signal by a delay time of 1H. In a state where the second switching circuit is producing one of the reproduced carrier chrominance signal and the delayed reproduced carrier chrominance signal, the second switching circuit is switched to produce the other of the reproduced carrier chrominance signal and the delayed reproduced carrier chrominance signal, responsive to the second switching signal (the output signal of the chrominance sequence discriminating circuit). The output signal of the second switching circuit is multiplexed with the reproduced luminance signal, and is supplied to the first switching circuit and to the 1H/2-delay circuit. As a result, a reproduced carrier chrominance signal having the correct chrominance sequence, is obtained from the second switching circuit.
However, in the conventional apparatus described heretofore, the delay time of the reproduced color video signal, that is, whether to delay the reproduced color video signal by the delay time of 1H/2 or not to delay the reproduced color video signal, is controlled responsive to the output detection signal of the 1H/2 skew detecting circuit. Moreover, the delay time of the reproduced carrier chrominance signal, that is, whether to delay the reproduced carrier chrominance signal by the delay time of 1H or not to delay the reproduced carrier chrominance signal, is controlled responsive to the output signal of the chrominance sequence discriminating circuit. Hence, it requires a complex analog signal processing in order to perform such control of the delay times. As a result, a circuit part for performing the analog signal processing occupies a large portion of the circuit in the apparatus, and it is difficult to make the circuit in the form of an integrated circuit (IC) and to perform the operations of the apparatus by use of a microprocessor.
Further, a rotary head for extended time mode play may be arranged extremely close to a rotary head for standard mode play. In this case, the two kinds of rotary heads are selectively used during the changed speed reproduction mode, and the noise bar which is generated when the reproducing rotary head scans over the reverse track, is greatly reduced. However, as will be described later on in the specification, a skew of 0.25H is generated in this case, and it is necessary to detect this skew of 0.25H in order to reduce the skew. But, it is difficult to stably detect the skew of 0.25H.